The quantity of liquid product dispensed and the quality of the spray pattern are critical parameters which have a substantial impact on the performance of a liquid product applied via an atomized spray. This is particularly true when the liquid product is being utilized as a thin film coating on a surface, and the total quantity of liquid product applied and quality of the spray pattern directly impact the thickness and evenness of the product coating.
In view of the ever-increasing awareness and concern among consumers with respect to the use of chlorofluorocarbon (CFC) propellants (now largely discontinued due to their impact upon the ozone layer) and volatile organic compound (VOC) propellants (which aggravate low altitude pollution problems, and many are highly flammable), there has been a trend away from pre-pressurized aerosol-type dispensing systems toward systems which utilize a manually-operated pump-type mechanism to force fluid through a specially-designed nozzle assembly to atomize the liquid product.
Comparatively higher viscosity liquid products present an additional challenge in terms of atomization, as the liquid has a tendency to resist break-up rather than being dispensed as a finely dispersed mist. As a general proposition, the less finely dispersed the spray produced, the more difficult is it to achieve a comparatively thin and uniform layer of product, and hence product effectiveness in use is correspondingly diminished.
While there are many products which may be applied in this fashion, one particular product application of current interest is in the area of oil-based fluid products used in food preparation, such as pan coatings and flavor enhancers. A thin, even coating of the oil-based product is desirable in order to provide for non-stick baking characteristics in the pan coating context and to prevent over-application of flavor enhancers. Such products usually comprise a vegetable oil and may optionally include a small quantity of additives for stability, performance, and flavor enhancement.
Some formulations require the addition of thinning agents such as water or alcohol in order to reduce the viscosity of the product to the point where it can be atomized with conventional spray technology. Such thinning agents are less than desirable from a consumer perspective because of their impact upon the performance of the product, the taste of the food product, and (with some thinners such as alcohol) the accompanying scent of the thinner. Other thinners such as water-based thinners may introduce microbial growth problems in the product.
While commercially available dispensing systems employing single-orifice, swirl-type atomizing nozzles may work satisfactorily with lower viscosity formulations, their performance with comparatively higher viscosity formulations suffers due to two major factors. First, viscous losses with comparatively higher viscosity fluids do not allow the fluid to attain enough swirl velocity to form a conical film. Second, the viscous nature of the fluid itself resists break-up of the fluid.
One currently commercially available pump sprayer for cooking oil products employs a nozzle design which produce two impinging jets of the product which collide outside the nozzle to atomize the liquid product. The performance of these spray systems suffers due to use of conventional pump technology which allows the product to emerge in a poorly atomized spray at the beginning and end of each pump stroke when the available pressure is less than required. Comparatively high viscosity fluids typically have a narrower window of operating pressures which will provide satisfactory atomization, with such operating windows becoming increasingly narrow with increasing viscosity. Under some circumstances, such as when the pump is slowly actuated, a higher viscosity product fails to be atomized at all, and emerges from the nozzle assembly in a fluid stream. This results in wasted product and oversaturation of the food item or baking surface to be coated. Heavy drippage of product from the sprayer may also occur, which is generally messy and unsanitary in a food preparation environment.
Accordingly, it would be desirable to provide a manually operated pump-type product delivery system which would provide for a well-atomized, finely-dispersed spray of product under all actuation circumstances even when higher viscosity formulations are utilized.